Pulmonary Function Testing

PFT Intro & Spirometry Basics - Kiddo Lung Check

• Purpose: Evaluate lung function; diagnose/monitor diseases (asthma, CF). Non-invasive.
• Spirometry: Measures air volume & flow during forced exhalation.
  • Key Parameters:
    • FVC (Forced Vital Capacity): Total air forcefully exhaled after max inspiration.
    • FEV1 (Forced Expiratory Volume in 1st sec).
    • $FEV_1/FVC$ Ratio: Normal > 0.8. Differentiates patterns.
    • PEFR (Peak Expiratory Flow Rate): Max flow rate.
  • Indications: Asthma, CF, neuromuscular disease, pre-op.
  • Interpretation:
    • 📌 Obstructive: ↓$FEV_1/FVC$ (e.g., Asthma). "Can't get air Out".
    • 📌 Restrictive: ↓FVC, normal/↑$FEV_1/FVC$ (e.g., Fibrosis). "Reduced lung volumes".

⭐ Cooperation is key: most children can perform reliable spirometry by age 5-6 years.

Spirometry Interpretation & Patterns - Airflow Clues

Key parameters: $FEV_1$ (Forced Expiratory Volume in 1s), $FVC$ (Forced Vital Capacity), $FEV_1/FVC$ ratio, $FEF_{25-75%}$ (Forced Expiratory Flow 25-75%).

• Obstructive Pattern:
  • $FEV_1$: ↓↓
  • $FVC$: N or ↓
  • $FEV_1/FVC$: < 0.7 (Key indicator)
  • $FEF_{25-75%}$: ↓↓ (Small airway disease)
  • Flow-Volume Loop: Concave/'scooped-out' expiratory limb.
• Restrictive Pattern:
  • $FEV_1$: ↓
  • $FVC$: ↓↓
  • $FEV_1/FVC$: N or ↑ (typically >0.7)
  • $FEF_{25-75%}$: N or ↓ (proportionate to $FVC$)
  • Flow-Volume Loop: Shrunken, "witch's hat" appearance; preserved shape but smaller. Peak flow ↓.
• Mixed Pattern:
  • $FEV_1$: ↓↓
  • $FVC$: ↓↓
  • $FEV_1/FVC$: < 0.7
  • Flow-Volume Loop: Features of both obstructive and restrictive.

⭐ A 'scooped-out' appearance on the expiratory limb of the flow-volume loop is characteristic of obstructive lung disease.

Lung Volumes & Bronchodilator Response - Puff & Proof

• Total Lung Capacity (TLC): Max air lungs hold. $TLC = VC + RV$.
• Vital Capacity (VC): Max air exhaled after deepest breath. $VC = TV + IRV + ERV$.
• Residual Volume (RV): Air left post-max exhalation. Measured by Helium dilution/Plethysmography. $\uparrow$ in obstruction.
• Functional Residual Capacity (FRC): Air after normal exhalation. $FRC = ERV + RV$. Resting lung volume.
• Tidal Volume (TV): Air per normal breath.
• Inspiratory/Expiratory Reserve Volume (IRV/ERV): Extra air inhaled/exhaled beyond TV.

Bronchodilator Response (BDR):

• Assesses airway reversibility, crucial for asthma diagnosis.
• Procedure: Baseline spirometry $\rightarrow$ Inhaled short-acting $\beta2$-agonist (SABA) $\rightarrow$ Repeat spirometry after 10-20 min.
• Positive Response (Children):
  • $\uparrow$ FEV1 by >12% from pre-bronchodilator value.
• 📌 Puff & Proof: Puff SABA, see Proof of reversibility.

⭐ A post-bronchodilator increase in FEV1 by >12% signifies significant reversibility in children.

Special PFTs & Clinical Links - Tiny Lung Detectives

• FeNO (Fractional exhaled Nitric Oxide):
  • Eosinophilic airway inflammation marker.
  • Predicts ICS response.

  ⭐ Elevated FeNO (e.g., >20 ppb in children) suggests eosinophilic airway inflammation and predicts ICS responsiveness.

• Impulse Oscillometry (IOS):
  • Measures airway resistance/reactance.
  • Minimal cooperation; for young kids.
  • Detects peripheral airway obstruction.
• Multiple Breath Washout (MBW):
  • Measures Lung Clearance Index (LCI).
  • Detects ventilation inhomogeneity.
  • Sensitive for early CF lung disease.
• CPET (Cardiopulmonary Exercise Test):
  • Assesses exercise limitation (cardiac/pulmonary).
  • Measures $V_{ ext{O}_2}$ max.
• Clinical Links:
  • Asthma: FeNO, IOS.
  • CF: LCI (MBW).
  • EIB: Exercise challenge with PFTs.

High‑Yield Points - ⚡ Biggest Takeaways

• Spirometry assesses airflow obstruction (e.g., asthma) and restriction (e.g., neuromuscular disease).
• FEV1/FVC ratio < 0.7 or < 5th percentile indicates obstruction.
• Reduced FVC with a normal or increased FEV1/FVC ratio suggests restriction.
• Bronchodilator reversibility (↑ FEV1 by > 12% and 200 mL) confirms asthma.
• Peak Expiratory Flow Rate (PEFR) is useful for monitoring asthma severity and response to treatment.
• Lung volumes (e.g., TLC, RV) help differentiate restrictive patterns and assess air trapping.
• Diffusion capacity (DLCO) is ↓ in interstitial lung diseases and pulmonary vascular disease.